1. Technical Field
The present invention relates to techniques for forming three-dimensional objects, and more specifically a technique for forming a three-dimensional object by ejecting a curable liquid to bind particles of powder material (powder).
2. Related Art
A technique has been known in which a three-dimensional object is formed by binding powder with a curable liquid. In this technique, the following procedure is repeated to form the three-dimensional object. First, a powder is spread to a uniform thickness to form a powder layer. Then, a curable liquid is ejected to desired positions of the powder layer to bind the powder particles. Consequently, only the portions of the powder layer to which the curable liquid has been ejected is bound, thereby forming a thin plate. This thin plate is hereinafter referred to as a “cross-sectional member”. Subsequently, another powder layer is formed to a small thickness on the previously formed powder layer, and the curable liquid is ejected to desired positions of the powder layer. Consequently, the portions of the new powder layer to which the curable liquid has been ejected are formed into a new cross-sectional member. Thin plate-like cross-sectional members are thus stacked one on top of another, thereby forming a three-dimensional object.
This three-dimensional object forming technique can easily be performed by binding a powder without preparing a die or mold as long as three-dimensional data of a desired form can be obtained. Accordingly, a three dimensional body can be quickly formed at a low cost. Since in the technique, thin plate-like cross-sectional members are stacked one on top of another, even a complicated shape having an internal structure can be integrally formed without assembling a plurality of parts, as described in Japanese Unexamined Patent Application Publication No. 2002-307562.
It is however difficult to form a three-dimensional object having smooth surfaces by this technique. More specifically, the curable liquid ejected to the powder layer permeates the powder in the depth direction and is simultaneously diffused in the transverse direction. Since the curable liquid does not uniformly permeate or diffuse, the surfaces of the object become rough. Also, the curable liquid permeating among the powder particles may be cured in a protruding manner, or powder particles not completely bound may fall off to form a recess in the object. The characteristics of the resulting object can be varied depending on the variation in binding rate (curing rate of the curable liquid). When the curable liquid can rapidly be cured, the powder can be bound so tightly that the resulting object is not easily deformed by some external force. However, the object is easily broken by a large external force. When the curing rate of the curable liquid is low, the resulting body is not easily broken by a large external force, but is liable to be deformed by a relatively small external force.